This invention relates to turbocharger shaft seal arrangements. More specifically, this invention relates to an improved seal arrangement for the turbine end of a turbocharger shaft for preventing passage of bearing lubricants into the turbine housing.
Turbochargers in general are well known in the art, and typically comprise a turbine wheel and a compressor wheel mounted on a common shaft and carried respectively within turbine and compressor housings. These turbine and compressor housings are in turn mounted on a so-called center housing which rotatably carries and supports the common shaft within suitable bearings and provides lubricant guide passages for circulating sufficient lubricant to the bearings to prevent excessive heat and wear. Of course, during operation of the turbocharger, exhaust gases from an engine rotatably drive the turbine wheel which, in turn, rotatably drives the compressor wheel for supplying compressed charge air to the engine.
In turbochargers, it is important to provide relatively leak-free seals between the shaft bearings within the center housing and the rotating turbine and compressor wheels. This is particularly true at the turbine end of the shaft, since the turbine typically operates in a relatively high temperature environment. Accordingly, it is desirable to prevent leakage of bearing lubricant into the turbine housing to prevent gumming and/or coking of the lubricant which can detrimentally affect turbine performance. Moreover, partial ignition of the lubricant within the turbine housing can have adverse effects on the level of pollutants discharged to atmosphere by an engine system.
Many prior art seal arrangements have attempted to reduce or eliminate leakage of lubricant out of a turbocharger center housing. The majority of these techniques involve the inclusion of one or more seal rings received with close tolerances about the shaft for sealing passage of the shaft through a center housing side wall into either the turbine or compressor housing. See, for example, U.S. Pat. Nos. 1,900,849; and 2,890,069. Other seal arrangements have attempted to vent the seal within the center housing in an effort to allow lubricant contacting the seal to drain therefrom. See, for example, U.S. Pat. Nos. 3,565,497; 3,834,156; 4,101,241; 4,107,927; and Japanese Utility Model Publication No. 48-26204. Still other designs have included a slinger or the like on the shaft for pumping excess lubricant within the center housing radially away from a seal ring. See, for example, U.S. Pat. Nos. 1,463,018; 3,053,541; 3,494,679; and 4,095,857. Further design arrangements have included relatively complicated labyrinth-type seal or packing seal constructions which may be combined with slingers or the like to provide a lubricant barrier arrangement. See, for example, U.S. Pat. Nos. 1,211,166; 2,910,328; and 3,004,782. However, these various prior art seal arrangements have not proven totally satisfactory, particularly during those conditions of turbocharger operation wherein a positive pressure differential exists between the center housing and the turbine housing. When such a positive pressure differential exists, available prior art seals such as those discussed above have shown an annoying tendency to leak lubricant into the turbine housing even at relatively low pressure differentials. The leakage problem is compounded by the effects of commonly encountered radial excursions of the turbocharger shaft during operation which tend to cause rapid wear of conventional seal ring devices whereby the requisite close tolerances are destroyed resulting in increased lubricant leakage.
This invention overcomes the problems and disadvantages of the prior art by providing an improved turbocharger shaft seal arrangement for the turbine end of the shaft having substantially improved resistance to leakage of the lubricant into the turbine housing.